The quickest and easiest way is to buy a new hard drive and clone it from the one the is currently installed.
Another way is to install the new drive, install the opeating system and then restore it from your backup.
What facilties do you have, backups?, external hard dribe enclosure?
Thanks. Useful information. I backup fairly regularly on an external hardrive using time machine. I suspect the sensible way forward would be to make sure I have a back up of everything I want. Then delete stuff that I don't use a lot from my Macbook to give me more storage for everyday things. I will probably renew my Macbook in a year or two anyway so probably not worth buying new internal hard drive. Thanks for your help.
For a new hard drive try Newegg.com http://www.newegg.com/Store/SubCategory.aspx?SubCategory=380&name=Laptop-Hard-Dr ives&Order=PRICE
Or OWC for regular hard drives and SSDs http://eshop.macsales.com/shop/hard-drives/2.5-Notebook/
Here are instructions on replacing the hard drive in a MacBook with a removable battery. http://creativemac.digitalmedianet.com/articles/viewarticle.jsp?id=45088
Here are video instructions on replacing the hard drive on the Aluminum Unibody
To transfer your current hard drive I like the free application SuperDuper. It makes a bootable copy of everything on your hard drive http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html You'll need a cheap SATA external hard drive case. Put the new drive in the case then format and partition the new drive and clone your old drive to the new one. Check that it's set up right by booting up from the external drive. Then replace your old hard drive with the new one and put your old one in the external case.
Here's a cheap SATA external hard drive case on Amazon http://www.amazon.com/Vantec-NexStar-2-5-Inch-External-Enclosure/dp/B002JQNXZC/r ef=pd_cp_pc_0
If you don’t have the tools to open up the MacBook OWC has a set for $5